Submitted to: Agricultural Experiment Station Publication
Publication Type: Experiment Station
Publication Acceptance Date: November 1, 2003
Publication Date: December 15, 2003
Citation: Baumhardt, R.L., Howell, T.A. 2004. Estimating grain sorghum production under deficit irrigation. Agricultural Experiment Station Publication. 4 p. Available: http://sorghum.tamu.edu/report_database/files/sub130hrby.BAUM_PRFT-03modl-rpt.pdf. Technical Abstract: Texas High Plains irrigated sorghum producers face difficult decisions that determine crop yield and production costs. These decisions are often based on individual experience; however, as the industry provides new irrigation and cultivar options, management selections include untested combinations. We are working to identify optimum long-term sorghum production practices from various combinations of irrigation amounts, available cultivars, and planting practices using the SORKAM computer simulation model and long-term (1958-1999) weather records from Bushland. As a first step to assure accuracy, we compared actual measured yields with modeled yields using known cropping and soil water conditions as input. Subsequently, grain sorghum yields were simulated using SORKAM for all possible combinations of cultivar maturity (early-15 leaf, medium-17 leaf, and late-19 leaf), planting date (15 May, 5 June, 25 June), population (48,000 and 60,000 plants/ac), row width (15 or 30 in), and irrigation capacity (approximately 2 and 4 gpm/ac). The SORKAM modeled yields using historical climate data as input show a complex relationship between irrigation levels, planting date, and cultivar maturity. That is, early maturing varieties achieve yields superior to medium and late maturing varieties when grown under limited irrigation; however, the late-maturing variety planted on 15 May and receiving 'full' irrigation yielded more than later planting dates or other cultivar combinations. Late planted grain sorghum often failed to reach physiological maturity or full potential yield compared with the typical 5 June planting date. Sorghum planted in narrow, 15 inch, rows increased grain yield 8% in comparison with conventional, 30 inch, row widths. Thus far, overall mean yield was unaffected by plant population since plant tillering offset differences in number of heads. Reports of these modeling results are being developed for subsequent distribution to the scientific community and agricultural producers.